( Reaffirmed 1998 ) Indian Standard CODE OF PRACTICE FOR INSTALLATION, MAINTENANCE AND OBSERVATIONS OF PORE PRESSURE MEASURING DEVICES IN CONCRETE AND MASONRY DAMS P'hRT I ELECTRICAL RESISTANCE TYPE CELL ( Second Reprint AFWL 1992 ) UDC 627.8.012.4:624.131.387 @ Copyright 1977 BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002 Gr 4 April 1977 IS : 8282 ( Part I ) - 1976 Indian Standard CODE OF PRACTICE FOR INSTALLATION, MAINTENANCE AND OBSERVATIONS OF PORE PRESSURE MEASURING DEVICES IN CONCRETE AND MASONRY DAMS PART I Hydraulic ELECTRICAL RESISTANCE Sectional TYPE CELL Committee, Structures Instrumentation BDC 60 Chuirmun Representing SHRI I. P. KAPILA Irrigation Works, Chandigarh Government of Punjab, A4embers DR B. K. AGARWALA SHRI S. S. ACJARWAL SHRI B. S. BHALLA SHRI M. L. KAUSHAL( Alrernafe CHIEF ENGINEER ( IRRIGATION ) National Physical Laboratory ( CSIR ). New Delhi Central Scientific Instruments Organization (CSIR). Chandiearh Beas Designs Organization, Nangal Township ) Public Works Department, Nadu Govcrnmcnt CA Tamil DIRECTOR ( INSTITUTE OF HYDRAULICS % HYDROLOOY) ( Alfernafe ) Koyna Project, Government of Maharashtra SHRI A. Y. DAFLE Central Water & Power Research Station, Punt DIRECTOR Idukki Project, Government of Kcrala SHRI C. En-v DARWIN SHRI N. BHWTHALINGA~I ( Alferrrare ) Central Water Commission, New Delhi SHRI S. N. GURU RAU SHRI M. T. GURNANI ( Alfernare ) SHRI N. S. GUJRAL f Alternate \ `Philips India Limited, Bombay SHRI P. GOSWAMI SHRI K. BASU ( AItcrnate ) Ram Ganga Project, Kalagarh SHRI R. C. GUPTA SHRI L. N. KABIRAJ Damodar Valley Corporation, Calcutta Vasi Shums & Co Pvt Ltd, Bombay SHRI Z. M. KARACHIWALA Meteorolo_rical Department, New Delhi Miss A. MANI Ministry of Irrigation & Power, New Delhi SHRI V. N. NAGARAJA Irri@ion & Power Department, Government SHRI P. K. NAGARKAR Maharashtra SHRI T. V. MARATHE( Alternate ) of ( Conrimted on page 2 ) @ Copyright 1977 BUREAU OF INDIAN STANDARDS This publication is protected under the Indian Copyrighf Act ( XIV of 1957 ) and reproduction in whole or in part by any means except with written permission of the publisher shall be. deemed to be an infringement of copyright under the said Act. IS : 8282-( Part I ) - 1976 ( Continued from prrgc 1 ) Members SHRI R.G. PATEL SHRI R. J. RAJU Representing . Public Works Department, Government of Gujaiat Irrigation Department. Government of Andhra Pradesh DR J. PIJRUSHOTHAM (Alternate) SHRI K. S. RAO Electronids Corporation of India Ltd. Hyderabad SECRETARY Central Board of Irrigation & Power. New Delhi DEPUIY SECRETARY (Alternate) SHRIH.C. VERMA Associated Instruments Manufacturers ( India ) Pvt Ltd, New Delhi SHRIK. G. PIJRANG( Alternate ) SHRID. A~HASIMHA, Director General, ISI ( Ex-oficio Member ) Director ( Civ Engg ) Secrerary SHRl G. RAhiAN Deputy Director ( Civ Engg ), IS1 IS : 8282 ( Part I ) - 1976 Indian Standard CODE OF PRACTICE FOR INSTALLATION, MAINTENANCE AND OBSERVATIONS OF PORE PRESSURE MEASURING DEVICES IN CONCRETE AND MASONRY DAMS PART I ELECTRKA-L RESISTANCE TYPE CELL 0. FOREWORD Standard ( Part I ) was adopted by the Indian Standards Institution on 39 November 1976, after the draft finalized by the Hydraulic Structures Instrumentation Sectional Committee had been approved by the Civil Engineering Division Council. 0.2 Stress and stability analysis of concrete and masonry dams is carried out by considering the existence of uplift across every horizontal plane, having uplift intensity-distribution in accordance with the design criterion in practice. The effect of the uplift is to induce instability on account of resulting buoyancy in weight of the material in dam above the horizontal section under consideration. 0.3 Provision of arrays of electric resistance type and vibrating wire type pore pressure cells in concrete and masonry at different elevations, and spaced at suitable distances from the upstream face, would provide information on the status of pore pressure at the time of observation. 0.4 Large concrete 0.1 This Indian and masonry dams are~provided with a row or rows of A record of the pore pressure development and its internal formed drains. variations would indicate the effectiveness and adequacy of these drains. At the same time, any sudden and significant variations in the pore pressure development may be indicative of some structural damage or deficiency in the dam material, warranting timely remedial measures being undertaken. 0.5 For measuring dams, the following a) Pressure the pore pressures device/instruments in the body of concrete are used: and masonry pipes; and b) Electrical pressure cells of two types, namely, electrical resistance type pore pressure cells, and vibrating wire type pore pressure cells. 3 IS : 8282 ( Part I ) - 1976 0.5.1 Pressure pipes and vibrating wire type pore pressure cells are proposed to be covered in separate standards. This standard covers the electrical resistance type pore pressure cells. 0.6 In the formulation of this standard due weightage has been given to international co-ordination among the standards and practices prevailing in different countries in addition to relating it to the practices in the field in this country. 0.7 For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test, shall be rounded of in ackordance with IS:2-1960*. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard. 1. SCOPE 1.1 This standard ( Part I ) covers the details of installation, maintenance and observation of resistance type pore pressure measuring devices in concrete and masonry dams. 2. INSTRUMENT 2.1 Electrical Resistance Type Pore Pressure Cell -Resistance type of pore prcssurc cell utilizes the two electrical principles, namely, changes in tension in elastic wires cause change in electrical resistance of the wires and changes in temperature of wires cause changes in electrical resistance of wires. Details of a typical pore pressure cell are shown in Fig. 1. This instrument has H solid steel diaphragm which is actuated by the pressure of the pore fluid which filters through a porous plug. The de5ection of the diaphragm is measured by means of a strain meter unit. The space between the porous plug and the diaphragm is filled with petroleum jelly or water before use so that the response is almost instantaneous. The readings are taken bv test set working on Wheatstone bridge principle and recorded on a s&table data form. 3. NUMBER AND LOCATJON 3.1 Representative blocks of the dam shall be selected for the installation of these cells. Generally the deepest over5ow and non-overflow sections are selected. The cells are installed in two or three levels in rows. The bottom row of pore pressure cells may be located a little above the foundation level (say about 1.5 m ) or as may be required by the desi_pn. ~The second row may be installed at one-third or half the height of the dam. The spacing of the ceils in each row may be 10 to 15 metres along the width of the dam. *Rules l%r rounding off numerical values ( revised). 4 IS : 8282 ( Part I) - 1976 1 PRESSURE CHAUBER FILLED WITH PETROLEUU JELLY OR WATER \-STEEL SLEEVE PRESS FIT FIG. I TYPICAL RESISTANCE TYPE PORE PRESSURE CELL 4; INSTALLATION 4.1 Prior to the embedment of pore pressure cells in the newly placed concrete or masonrjt, each instrument should be thoroughly checked for cell resistance as also for the lead resistance and these should be entered in the pro forma given in Appendis A. The resistance and `rcsistancc ratio before splicing and after splicin, `*should also be recorded in the pro forma given in Appendix A which is meant for recording pre-embcdmcnt test results. 4.2 The pore pressure cells are usually located near the top of a lift, where placement can be accomplished after concreting in the area has been completed. A hole just large enough~to accommodate the instrument and The cell should about 300 mm deep should be dug at the desired location. be laid horizontally in the hole, normal to the exterior surface of the concrete and with the porous plug at the desired distance from the upstream surface. 4.2.1 Frames or brackets to hold the cell in position during embedment, should not be used, since they would possibly provide a lenkage path directly to the cell. Concrete or mortar as the case may be, should be placed by hand around the instrument and tamped lightly so as to obtain contact between the body of the cell and the surrounding concrete/masonry. Excessive tamping of the concrete/masonry shall be avoided as this would result in a highly impermeable zone around the cell and affect the normal build-up of hydro-static pressure. After embedment, a temporary cover of boards laid over the cell locations will afford protection until the concrete/ mortar has hardened. The ends of cables attached to the pore pressure cells which remain uncovered for a while until these are properly terminated in a terminal board, shall be protected by cable protection caps, This pre-caution is considered necessary with a view to prevent moisture and water entering the pore pressure cells through the cable ends. 5 IS : 8282 ( Part I ) - 1976 4.3 Cables and Conduits 4.3.1 The pore pressure cells are normally supplied with about 750 mm of three conductor rubber covered cable attached to the instrument. Enough additional three conductor cable is then added in the field to reach from the point where the instrument is embedded to a terminal station in the gallery. The additional length of cableshall be attached to the pore pres$ure cells by means of splicing in accordance with the `Indian Standard Code of practice for selection, splicing, installation, and providing protection to the open ends of the cable used for connecting resistance type measuring devices in concrete and masonry dams' (.under prepararian ). NOTE-Till such time the standard under preparation shall be as agreed upon between the concerned parties. is published, the matter 4.3.2 In estimating the length of the cable to be added, a suitable route between the point of embedment of the instrument and the terminal station in the gallery should be selected by a study of the drawings. In selecting the route, due consideration shall be given to the construction procedures involved in placing the concrete/masonry where the instrument is to be embedded and to possible obstructions along the chosen route. After the selected route has been verified the .length of the cable required shall be estimated, and a small amount usually 10 percent or 2 m, whichever is larger. shall be added to all,ow for extra length required due to normal The length of.the cable should be variatiops from the seledted route. limited as far as possible. In any case it shall not exceed 80 m. 4.3.3 In general, cables run horizontally without conduit in the concrete and in conduits in the masone and run in downward and upward directions in conduits both in the concrete and the masonry. The conduit may be of any material which will not collapse in the fresh concrete/ The size of the conduit may be chosen in accordance with the masonry. procedure given in the `Indian Standard Code of practice for selection, splicing, installation, and providing protection to the open ends of the cable used for connecting resistance type measuring devices in concrete and masonry dams' ( z&er preparation ) ( see Note untieer 4.3.1 ). 4.3.4 If the cable leads are to cross, contraction joints in the structure, a slack cable recess shall be provided at the crossing point. This may consist of a wooden box block out, forming a recess into which the cable is run. During placement of concrete/masonry in the adjacent block, a 300 mm loop of slack cable shall be left in the unfilled block out and the remaining length of cable laid in theusual manner. 4.3.5 Cables should be threaded individually into the conduit, so that each cable will be required to support only its own weight. At the entrance of the cables into the conduit suitable protection, such as padding with burlap, should be provided around each cable and in the interstices between the cables to prevent sharp bends and to prevent the entrance of concrete,' mortar and grout into the conduit. IS : 8282 ( Part I ) - 1976 43.6 Where a group of cables is to be run horizontally in a concrete lift, they may be taped together at intervals and laid on the top of the last abut one layer -of concrete in the lift, covered with pads of fresh concrete/ mortar at several points along their length, and placement of the final concrete lift layer allowed to proceed in the normal manner. 43.7 The layout should be so planned in the same block as far as possible. that cells and terminal boards are 4.3.8 In cases where a number of cables from widely-separated points are collected at one central point and run downward into a conduit, a very successful plan is to run the cable in two steps. A collecting box or concrete form is erected around the grouped conduits so that the lifr is left During the placement of the concrete about 450 mm low at the conduits. in which the cells are embedded, the cables are brought horizontally to the collection point and there coiled and hung out of the fresh As soon as the concrete has set sufficiently to bear traffic, concrete. the cable -coils are taken down the conduit to the terminal boards. The advantages are that it is much easier to sort and run cables when they are not muddled with fresh concrete/mortar. 4.4 Identification of Cables and Cells - Each cell should be identified by a letter prefix designating the type of instrument and numbered consequently. The normal prefix used for pore pressure cells is PP. When the cable lead is coilnected to a-cell, -an identification band with the instrument identification. number stamped or punched on it is crimped to the cable about 900 mm from the cell and a similar band crimped about 300 mm from the free end of the cable. In addition a few more markers, consisting of the identification number marked on white tape and covered with linen zind friction tape, should be placed around the cable near the reading end. 4.5 Terminal Boards facilities for making 4.5.1 Location of Terminal Boards - Permanent readings are provided in terminal recess usually located in blockouts on walls of galleries nearest to the instruments. The reading stations for all embedded instruments in a monolith should be located in that monolith if joints. possible, in order to avoid runnin, 0 cable leads across contraction Separate terminal recesses for cable leads from different types of instruments are not required. Where a gallery or similar semi-protected locaticn is not-available, a conveniently accessible exterior location may be selected, and the facilities secured against unauthorized tampering. 4.5.2 Lighting - Normal supplementary fixture for reading station. gallery lighting lighting should is usually not adequate and a be provided at the terminal 4.53 Moisture Prevention - To reduce corrosion at the cable terminals and panel board connections, usually a serious problem in dam galleries, an .7 Is : 8282 ( Part I) - 1976 electrical strip heater or incandescent lamp permanently kept on should be A bulb provided in the recess for installed within the terminal recess. lighting may also serve this purpose. 4.5.4 Installing Terminal Equipment - After all cable leads have been brought into a terminal recess the surplus lengths of cables should be cut off and the end of individual conductors prepared for permanent connection to the panel board or terminal strip. Proper care shall be taken for identification of the cables and cells ( see 4.4 ). 5. COLLECTION OF COMPLEMENTARY DATA to structural 5.1 The collection of related and supportin g data pertaining behaviour is an integral part of the instrumentation programme, and should proceed concurrently with the installation of the instruments and the Tvnes of information reauired to readings of the embedded instruments. observatidn resultsinclude the foilowing: support or clarify the instrument a) Construction Progress - schematic concrete/masonry gram showing lift placement dates, concrete placing and lift thickness. contents, b) Concrete Mixes - cement typical combined aggregate gradings mixes. c) Fine Aggregate mixing. d) Air Entrainedintroduced. typical fine aggregate amount of entrained water-cement for interior gradings, air, physical placing diatemperatures ratios, and and exterior before and after use, how pro- admixture and e) Cement TJJpe- source or sources, perties, including heat of hydration. chemical geologic classification, f ) Aggregates -types, tion, sources, and chemical properties. petrographic descrip- and method of curing, g) Curing and Insulation -type and duration of insulation protection, if any. h) Pool Elevations j) Foundation features. daily reservoir final and tailwater elevations, type, location elevations. unusual geologic Conditions - rock Much of the information listed above will usually be available from investigations carried out prior to and during the project design stage or will be obtained under usual construction control operations. IS : 8282(Part I ) - 1976 5.1.1 Observers should be alert to detect cracks or similar evidences of structural distress which may develop; and record time of occurrence, initial size and extent and subsequent ,changes in size and extent, and any corrective actiontaken. -6. OBSERVATIONS 6.1 The readings of resistance of the steel music wire of the cell and the resistance ratio should be measured using the test set working on the Wheatstone bridge principle. 6.2 The observations of the pore pressure cells should begin as soon as the instruments are covered and may continue at gradually increased time intervals. The pore pressures within concrete/masonry develop slowly and occur only when hydrostatic head is sustained for an extended period The pore pressure cells against the upstream concrete/masonry surface. may be read initially at 1 to 3 h after embedment and subsequent readings may be taken at weekly intervals after the reservoir level reaches the level of the instruments and until the operatin, 0 reservoir elevation has been attained and twice monthly thereafter. 7. RECORD OF OBSERVATIONS AND METHOD OF ANALYSIS 7.1 The observations made of the embedded cells shall be suitably recorded. A recommended pro forma for the record of observations and for transfer of observations to a permanent record in the ofTice is given in Appendices B and C. These data sheet forms may be got printed in advance upon which the observations can be noted as they arc taken and The method of analysis of the for preparation of permanent records. data obtained by the observations of embedded pore cells -is given in Appendix C. 8. SOURCES OF ERROR against in 8.1 The following are the sources of error and should be guarded the measurement of resistance type~pore pressure cells: 4 Low voltage of test set batteries; b) Loose connection of cable terminals on terminal cl Loose connections in the test set circuit; 4 High voltage resulting in heatin g of the wires the accuracy of the reading; and panels; and thus affecting e) Imperfect cable splice, resulting from improper matching of individual conductors, improper soldered connections or splice not rendered moisture-proof. 9 IS:82tii(PartI)-1976 APPENDIX ( Clause 4.1 ) A PRO FORMA FOR THE RECORD OF OBSERVATIONS RESISTANCE TYPE PORE PRESSURE CELLS PREEMBEDMENT TESTS Project . . .. -.-............... Instrument No. *. . . . . . . . . . Air temperature . . . . . . . . . . . . . . . ..- . . . Wet bulb temperature.. .......... Manufacturer's No.. ............ Project No.. ....................... Location .............................. 1. RESISTANCE BEFORE CABLE SPLICING ii) White-green iv) Resistance one pair ONLY ) i) White-black iii) Green-black 2. RESISTANCE RATIO (INSTRUMENT i) Direct ratio ( white-green-black ) ii) Revcrsc ratio ( black-green-white ) 3. INDIVIDUAL i) Length CONDUCTOR RESISTANCE ii) Black iii) Green iv) White OF INSTRUMENT AFTER GABLE SPLICING ii) White-green iv) Resistance one pair WITH CABLE) 4. RESISTANCE i) White-black iii) Green-black 5. RESISTANCE i) Direct ratio ( white-green-black ) ii) Reverse ratio ( black-green-white) Date of test: Date of embedment: NOTES: RATIO ( INSTRUMENT Name and signature of observer 10 APPENDIX ( Clause 7.1 ) PRO FORMA1;ORPERhIANENT RESlSTANCE C OF OBSERVATIONS tj .. ii! G 3 E I TYPE PORE l'RESSURE RECORD CELLS Sheet No *. . . . . . , . . . . . . . . . . . . . . . . . . . . . Location . . . . ..I...&.................... Project . . . . . . . . . . . ..I.................... Pore Pressure Cell No... . . . . . . . . . . . Calibration Data: G 2 K Cell resistance at A'C* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (B* ) bhms Charlge in temperature per ohm change in resistance . . . . . . . . . . . . . . . . . . ..a............ (c*) "c! Ratio at zero stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . % Original calibration constant . . . . . . . . . . . . . . . . . . . . . . . . ..- (*) N/m* (kg/cmt) per 0.01% ratio change Calibtation constant corrected for leads . . . . . . . . . . . . . . . ( D) N/m2 ( kg/cm4) per 0'01% ratio change Resistance of leads at . . . . . . . . . . _. . . . . . . "C . . . . . . . . . . . . . . . . . . ohms (pair) DATE TlhiE TEMCELL TOTAL LEAD RESISTANCE RESISTANCE RESISTANCE PER$FRE OIlhiS OHhlS OIthlS (3) (4) (5) (6) RESISTANCE cM;;,lN RY" 0 (7) % V-Y INDICATED REMARKS HYDROSTATIC PRESSURE N/m* \$/cm9 (1) (2) (10) *Calibration data furnished by the manufacturer. Explnnntions Cal 3 co1 4 for columns including nnnlyris: Total resistance of cell as tncnsured in the field. directly, and this column may be left blank. Resistnncc of tlic white and black conductors, With a 4-conductor as measured cable the cell resistance is measured nltcrnativc a reasonably nccurate vnlue mny be detcrnrincd by subtracling lhe ldtal resistance and expansion coils measured measured separately. co1 5 co1 6 co1 7 Co1 8 co1 9 t; Resistance directly during the splicing operation. As an of the contraction in series from the sum of the resislances of the contraction and expansion coils It is obtaintd by subtracting co1 4 from col 3. in co1 5, multiplying the diflerence of cell excluding cable leads. Temperature of the cell, obtained by subtracting by (C) and adding the product to (A). The resistance ratio of the cell as measured (II) from the cell resistance with the test set. after the Total change in resistance ratio (col 7 ) from a selected initial value, usually the first reading concrete'masonry has hardened or at about 24 h age. Proper algebraic sign should be shown. Multiply values in col 8 by the corrected calibration constant (D). Negative viilues of the ratio changes (co1 8) indicate positive pore pressures. Except for minor ratio variation prior to the development of significant pore pressures, the cell will not respond reliably IO negative pressures, and all entries in co1 9 will represent pore pressures above the oil pressure in the cell chamber which will be approximately atmospheric. NOTE- No temperature corrections are made; but the temperature data obtained is of general interest and provide a possible means for detecting faulty operation of strain measuring units installed in the vicinity of the pore pressure cells. Manak Bhavan, 331 9 Bahadur 01 31, Shah Zafar Marg. 331 13 75 NEW DELHI Telegrams: ( Cammon 110002 Manaksanstha to all Offices) Telephone I 331 01 31 Telephones: Regional Central Offices: : Manak Bhavan, 9 Bahadur Shah Zafar Marg, NEW DELHI 110002 *Eastern : l/l 4 C. I. T. Scheme VII M, V. I, P. Road, Northern Maniktola, CALCUTTA 700054 : SC0 445-446, Sector 35-C. CHANDIGARH 160036 331~13 75 36 24 99 I Southern twestern : C. I. T. 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